Semiconductor on insulator (SOI) devices can have carriers in the bulk due to the drain hot carrier effect. In floating body devices, these carriers can forward bias the source-body p-n junction and cause a “kink” effect and self-latching. Additionally, a parasitic bipolar transistor can thus be turned on.
The kink effect generally results in the appearance of a kink, or discontinuity, in the output characteristics of an SOI MOSFET operating in strong inversion. The kink effect can be very strong in n-channel transistors, but is usually absent from p-channel devices. In affected devices, when the drain voltage is high enough, the channel electrons can acquire sufficient energy in the high electric field zone near the drain to create electron-hole pairs, generally due to an impact ionization mechanism. The generated electrons move into the channel and the drain. On the other hand, the holes, which are majority carriers in the p-type body, migrate towards the place of lowest potential, i.e. the floating body. This injection of holes into the floating body can forward bias the source-body junction. It is necessary, therefore, to remove or recombine the carriers in order to prevent the ill effects thereof.